Journal
JOURNAL OF FLUORESCENCE
Volume 21, Issue 4, Pages 1683-1687Publisher
SPRINGER/PLENUM PUBLISHERS
DOI: 10.1007/s10895-011-0860-0
Keywords
beta-lactoglobulin; Tryptophan residues; pH; Fluorescence lifetimes; Fluorescence emission spectra; Fluorophore sub-structures
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Origin of tryptophan residues fluorescence in beta-lactoglobulin is analyzed. Fluorescence lifetimes and spectra of beta-lactoglobulin solution are measured at pH going from 2 to 12 and in 6 M guanidine. Tryptophan residues emit with three lifetimes at all conditions. Two lifetimes (0.4-0.5 ns and 2-4 ns) are in the same range of those measured for tryptophan free in solution. Lifetimes in the denatured states are lower than those measured in the native state. Pre-exponential values are modified with the protein structure. Data are identical to those already obtained for other proteins. Fluorescence lifetimes characterize internal states of the tryptophan residues (Tryptophan sub-structures) independently of the tryptophan environments, the third lifetime results from the interaction that is occurring between the Trp residues and its environment. Pre-exponential values characterize substructures populations. In conclusion, tryptophan mission occurs from substates generated in the excited state. This is in good agreement with the theory we described in recent works.
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